I have a 14 year old grandson who has just been diagnosed diabetic and put on insulin. Given the strong history of diabetes in our family, is there a reasonable probability that he has MODY, and what questions should be asked of his general physician?

He is overweight - perhaps by a factor of 2. His father is free of
diabetes - as yet - but I expect him to get it. I am diabetic, as is my
sister, my sole surviving sibling. My father was diabetic, as were two of
his four siblings. Both my grandparents on my father's side, and several of
their siblings were diabetic. Furthermore, the boys mother is half
American Indian.

Answer:

The combination of a family history affecting both males and
females over five generations together with the obesity makes it quite
likely that your grandson has one or other of the forms of Maturity-Onset Diabetes of the Young (MODY).

At the moment, the most important goal is to achieve the best
possible control of his blood sugar rather than to be overly concerned for
a precise diagnosis. Nevertheless I can see some reasons why it might be
worth the time and expense to achieve an exact diagnosis. The first is for
prognosis. MODY2 or glucokinase deficiency, a chromosomal abnormality on
chromosome 7, usually has a mild course with a minimal tendency to
vascular complications and usually doesn't require insulin. Several
variants of this genetic abnormality have now been described. MODY1 and
MODY3 are chromosomal abnormalities on chromosomes 20 and 12 of what are
called the hepatocyte nuclear factors 4a and 1a. These forms of MODY
are more vulnerable to long term complications and more likely to need
insulin.

A second reason for exact diagnosis could be for genetic
counselling within the family.

The third reason, of course, is to explore the possibility that your
grandson may not require insulin after all. Perhaps the most expeditious
way to deal with this is to ask your doctor about getting an
antibody
test and details of how to get this done can be obtained for the DPT-1
office at (800) 425-8361. If he has antibodies he has autoimmune Type 1 Diabetes and will need insulin for the rest of his life or until
transplants become greatly more practicable. If he is antibody-negative,
then the possibility of confirming MODY is increased especially if there
is any African American or Hispanic inheritance in the family. Because
there is no element of insulin resistance in any of the forms of MODY the
next stage in diagnosis would be to do an intravenous glucose tolerance
test with insulin levels and a test of insulin secretion rates during a
graded glucose infusion. This would enable a differentiation from
Type 2 Diabetes. Such a plan would almost certainly have to be
negotiated in a specialised research Center and so of course would the
ultimate
determination of a specific chromosomal abnormality.

Finally, MODY is uncommon, probably less than 1% of all diabetics
below age 20; but a significant proportion undiagnosed. Amongst all
insulin dependant diabetics this group comprises 2-5%.

I hope this gives you a glimpse of the complexity of diagnosis;
but also gives some encouragement to see if insulin may not be absolutely
necessary for good control.

Additional Comment from Dr. Lebinger:

If your grandson had ketones in the urine and had already lost some
weight when he was diagnosed with diabetes, most likely he does not have
a form of MODY and will need insulin treatment. If he did not have
ketones in the urine and had not lost any weight prior to diagnosis,
then further testing is necessary to decide if he has a form of MODY or
early Type 1 (Insulin Dependent) Diabetes.

[Editor's comment: It's not clear from your question if your grandson has
been under the care of a pediatric endocrinologist as well as a General
Practitioner. If he's not, he ought to be. This is a rare situation, and
requires specialized evaluation, as discussed by Dr. O'Brien in his
answer.
WWQ]

Original posting 8 Jun 97

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Last Updated: Tuesday April 06, 2010 15:08:54
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